Optical member and method of producing the same

ABSTRACT

A plurality of optical members (lenses) for use in ultraviolet region are mutually stuck. A fluorine-based organic compound (for example, fluorine-based oil) is provided between them. The periphery of the optical members is sealed with a sealant. As the sealant, an adhesive fluorine resin, for example, a soluble fluorine resin is used.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical member for use inultraviolet region (for example, an optical member for use in atransmitting optical system such as laminated lens or prism) and amethod of producing the same and, particularly, to an optical membersuitable for use in the ultraviolet region of a semiconductor inspectiondevice or the like and a method of producing the same.

[0003] 2. Description of the Related Art

[0004] In conventional semiconductor inspection devices and otheraccurate measuring devices, inspection of a wafer or the like has beenperformed in an ultraviolet wavelength area of 200-400 nm, and a quartz(SiO₂)-made lens or a fluorite (CaF₂)-made lens is used in suchsemiconductor inspection devices for correction of chromatic aberration(achromatization).

[0005] For example, as shown in Japanese Patent Application Laid-OpenNo. 60-186444, it is known to protect the boundary part of the adhesivesurface of a prism type optically adhered beam splitter forinterferometer with the outside with a sealant.

[0006] An optical element having an adhesive member constituted as afilm having both a film thermal adhesive layer and a barrier layer byusing a thermally fusible film with high steam barrier property such asfluorine-based film is known as shown in Japanese Patent ApplicationLaid-Open No. 2-287419, wherein CTFE (polychlorotrifluoroethane), FEP(polyperfluoroethylene-propylene), PVDF (polyvinylidene fluoride), PVDC(polyvinylidene chloride) and the like are used as the material of thefilm.

[0007] Further, as shown in Japanese Patent Application Laid-Open No.60-176017, an optical element in which a rubber elastic body such asethylene propylene rubber or silicone rubber which is transparent undervisible light is put between two lenses which are not closely fitted,and the rubber elastic body is covered with a piezoelectric film such aspolyvinylidene fluoride or the like is known.

[0008] In Japanese Patent Application Laid-Open No. 5-2105, as thematerial of an annular film constituting the film material, for example,thermoplastic resins and thermosetting resins such as polyethylene,polypropylene, polyvinyl chloride, polyamide, polystyrene,polyisobutylene, polycarbonate, polyvinilydene chloride, polyvinylacetal, polymethyl methacrylate, polyacrylonitrile, polyimide,cellulose-based fluorine resin, epoxy, polyurethane, silicone resin;copolymers thereof, and those with plasticizer or filler added theretoare used.

[0009] As shown in Japanese Patent Laid-Open No. 2003-12349, a joinedoptical element for UV region is also known, which is formed through anadhesive layer by joining optical elements capable of transmittingultraviolet rays, using as the adhesive layer a solution in which asolvent-soluble organic fluorine resin having no unsaturated bond in themolecule is dissolved in a fluorine-containing solvent having a boilingpoint of 150° C. or higher and containing no unsaturated bond in themolecule, vaporizing the solvent in the part in contact with atmosphereof the adhesive layer, and joining the optical elements in the statewhere the solvent in the other part is left in the adhesive layer.

[0010] The adhesion by use of a conventional sealant had problems asthat the inside solvent is not hardened because it is not vaporized dueto large adhesion distortion, a heating treatment cannot be performedbecause it affects a high precision lens, and an axial slippage iscaused. Therefore, an extremely precise device such as semiconductorinspection device could not be suitably used in ultraviolet region.

SUMMARY OF THE INVENTION

[0011] In consideration of the above problems, the present inventionthus has an object to provide an optical member sealed with a sealantnever deteriorated by UV absorption and capable of precisely mutuallybonding optical elements or the like and a method of producing the same.

[0012] Preferred modes of the present invention are then described.

[0013] A plurality of optical members for use in ultraviolet region areclosely fitted and stuck together. A fluorine-based organic compound isfilled between the optical members. The periphery of the fluorine-basedorganic compound is sealed with an adhesive fluorine resin, e.g., asoluble fluorine resin in the periphery of the optical members.

[0014] A preferred sealant is a sealant which is never deteriorated byultraviolet absorption, causes no adhesion distortion when covering theoptical elements, so that the inside solvent can be easily vaporized andhardened without requiring a heating treatment, nor axial slippage. Asthe most suitable material to be filled in the optical elements for usein ultraviolet region, a fluorine-based organic compound is adapted. Apreferred example of the fluorine-based organic compound is afluorine-based oil (fluorine grease).

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic sectional view of an optical memberaccording to one embodiment of the present invention; and

[0016]FIG. 2 is a schematic sectional view of an optical memberaccording to the other embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be further described in reference tothe drawings.

[0018]FIG. 1 shows an optical member according to one embodiment of thepresent invention.

[0019] In FIG. 1, the optical member comprises two lenses 1 and 2 foruse in ultraviolet region.

[0020] The lens 1 is a lens formed of a fluorite (CaF₂) about 20 mm indiameter, and the lens 2 is a lens formed of a synthetic quartz (SiO₂)about 20 mm in diameter. A gap entirely having the same thickness ispreferably provided between the lenses 1 and 2. A fluorine grease 3 thatis one preferred example of the fluorine-based organic compound isperfectly filled in the gap. Consequently, the lenses 1 and 2 aremutually closely fitted and stuck.

[0021] The dimension of the gap between the lenses in FIG. 1 is set to10-20 μm.

[0022] The profile irregularities of the fluorite (CaF₂) lens 1 and thesynthetic quartz (SiO₂) lens 2 are, for example, about 1/20 λ, wherein λshows a standard wavelength, and it is set, as described later, to awavelength of transmitted ultraviolet rays 200-300 nm, for example, 248nm.

[0023] A wavelength of 100-200 nm, for example, 193 nm is also possibledepending on the power of laser.

[0024] The fluorine grease 3 has durability to an excimer laser such asKrF laser described later.

[0025] As the fluorine grease 3, various ones are usable. Particularly,the fluorine greases described below are preferably used. However, thepresent invention is never limited by them.

[0026] It was found that, when the lenses 1 and 2 stuck as shown in FIG.2 are irradiated with a high luminance ultraviolet ray having a shortwavelength of 200 nm or less, the surface of the synthetic quartz lenses1 and 2 in contact with the fluorine-based grease 3 as the fluorine oilare roughed. The roughing of the surface of the synthetic quartz lenses1 and 2 can be prevented by evaporating fluorides 5, 6 such as magnesiumfluoride on the surface of the synthetic quartz lenses 1 and 2.

EXAMPLE 1

[0027] Fluorine grease produced by Daikin Industries Ltd. (trade name:DEMNUM Series)

EXAMPLE 2

[0028] Fluorine grease produced by E.I. du Pont de Nemours & Company

EXAMPLE 3

[0029] Fluorine grease produced by Solvay S.A. (trade name; FOMBLINY)

CF₃O—CF₂—CF₂O—CF₂_(q)O—CF₃

[0030] In the embodiment of FIG. 1, the fluorine grease produced byDaikin Industries, Ltd. is used.

[0031] In the state after the fluorine grease 3 is filled between thelenses 1 and 2, the total thickness of the fluorite (CaF₂) lens 1, thefluorine grease 3, and the synthetic quartz (SiO₂) lens 2 is about 5 mmalthough it is exaggerated in FIG. 1.

[0032] As shown in FIGS. 1 and 2, after the fluorine grease 3 is filledin the gap between the fluorite (CaF₂) lens 1 and the synthetic quartz(SiO₂) lens 2, the whole periphery of the lenses 1 and 2 is sealed witha sealant 4.

[0033] As the sealant 4, for example, organic solvent-soluble amorphousfluorine resins such as CYTOP (trade name, produced by Asahi Glass Co.,Ltd.), TEFLON (registered trademark), AF Series (trade name, produced byDu Pont-Mitsui Fluorochemicals Company, Ltd.), ALGOFLON AD series (tradename, Solvay Solexis K.K.), INT-444V (trade name, produced by NImaterial), and other products produced by Hoechst AG and MitsubishiRayon Co., Ltd. can be used. In this case, the fluorite (CaF₂) lens 1and the synthetic quartz (SiO₂) lens 2 can be more firmly bonded, andthe leak of the fluorine grease 3 from the periphery of the gap betweenthe lenses 1 and 2 can be surely prevented.

[0034] In addition to these fluorine-based oils, as the samefluorine-based organic compounds, AFLUDE (trade name, produced by AsahiGlass Co., Ltd.), other perfluorocarbons (PFC, produced by 3M Companyand E.I. du Pont de Nemours & Company), hydrofluorocarbons (HFC),hydrofluoroether (HFE), DEMNUM (produced by Daikin Industries, Ltd.),FOMBLIN (produced by Solvay AG), KRYTOX (produced by E.I. du Pont deNemours & Company) and others can be also used for the production of anoptical member for use in ultraviolet region.

[0035] [Experiment]

[0036] An optical member was produced by sticking two lenses 1 and 2 asshown in FIG. 1. The optical member was irradiated with an excimer lasersuch as KrF laser of deep UV 248 nm from a general direction at anoutput of 3 W/cm² for 148 hours. The optical thickness of the fluorinegrease 3 was 10 μm, but the transmittance of the fluorine grease 3 washardly changed. Adhesion distortion was hardly observed.

[0037] [Comparative Experiment]

[0038] An optical member having the same shape and dimension as theoptical member used in the above experiment (e.g., the same diameter,thickness and clearance between lenses 1 and 2) was produced byperforming the adhesion of fluorite (CaF₂) lens and synthetic quartz(SiO₂) lens by use of an adhesive consisting of an organic siliconeresin of SILPOT 184 produced by Dow Corning Corp. instead of filling thefluorine grease 3 in the gap between the lenses 1 and 2. The opticalmember for comparative experiment was irradiated with an excimer lasersuch as KrF laser of deep UV region 248 nm at an output of 3 W/cm² for148 hours similarly to the above experiment. Consequently, the layerformed by the adhesive consisting of the organic silicone resin ofSILPOT 184 produced by Dow Corning Corp. was peeled as it is burnt offby the laser beam of the excimer laser, and deteriorated. Adhesiondistortion was also caused to deteriorate the characteristics of theoptical member.

[0039] According to the present invention, a plurality of lenses can befurther firmly and precisely joined, and the leak from the periphery ofthe gap between the lenses can be surely prevented. Further, thedeterioration by UV absorption can be also avoided.

What is claimed is:
 1. A method of producing an optical member,comprising steps of: sticking a plurality of optical members for use inultraviolet region; filling a fluorine-based organic compound betweenthe optical members; and sealing the fluorine-based organic compoundwith an adhesive fluorine resin at the periphery of the optical members.2. The method of producing an optical member according to claim 1,wherein the fluorine-based organic compound is a fluorine-based oil. 3.An optical member comprising: a plurality of mutually stuck opticalmembers for use in ultraviolet region; a fluorine-based organic compoundprovided between the optical members; and a fluorine resin foradhesively sealing the periphery of the fluorine-based organic compoundat the periphery of the optical members.
 4. The optical member accordingto claim 3, wherein the fluorine-based organic compound is afluorine-based oil.